Property, Plant and Equipment - Components of Property, Plant and Equipment (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Land	$ 2.0	$ 2.0
Building and improvements	37.0	29.6
Pipeline and equipment	888.2	895.7
Other	15.5	16.9
Property, plant and equipment, gross	942.7	944.2
Accumulated depreciation and amortization	(368.1)	(354.8)
Property plant and equipment excluding construction in progress	574.6	589.4
Construction in progress	34.3	21.2
Property, plant and equipment, net	608.9	610.6	[1]
Operating leased assets, cost	163.4
Costs related to assets under capital lease	22.8	22.8
Accumulated depreciation on assets under operating lease	32.1
Accumulated depreciation on assets under capital lease	$ 2.7	$ 1.6
Building and Improvements | Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life	10 years
Building and Improvements | Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life	40 years
Pipeline and Equipment | Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life	10 years
Pipeline and Equipment | Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life	30 years
Other | Minimum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life	5 years
Other | Maximum
Property Plant And Equipment [Line Items]
Property, plant and equipment, depreciable life	25 years

[1] Prior period financial information has been retrospectively adjusted for the acquisition of the Shell Delta, Na Kika and Refinery Gas Pipeline Operations.